Buried anode lithium thin film battery and process for forming the same

ABSTRACT

A reverse configuration, lithium thin film battery ( 300 ) having a buried lithium anode layer ( 305 ) and process for making the same. The present invention is formed from a precursor composite structure ( 200 ) made by depositing electrolyte layer ( 204 ) onto substrate ( 201 ), followed by sequential depositions of cathode layer ( 203 ) and current collector ( 202 ) on the electrolyte layer. The precursor is subjected to an activation step, wherein a buried lithium anode layer ( 305 ) is formed via electroplating a lithium anode layer at the interface of substrate ( 201 ) and electrolyte film ( 204 ). The electroplating is accomplished by applying a current between anode current collector ( 201 ) and cathode current collector ( 202 ).

CONTRACTUAL ORIGIN OF THE INVENTION

The United States Government has rights in this invention pursuant toContract No. DE-AC36-99GO-10337 between the United States Department ofEnergy and the Midwest Research Institute.

TECHNICAL INVENTION

This invention relates to the fabrication of lithium thin film secondarybatteries.

DISCLOSURE OF INVENTION

Batteries are galvanic electrochemical cells which store and supplyelectrical energy as a product of a chemical reaction. In their simplestconceptualization, batteries have two electrodes, one that supplieselectrons by virtue of an oxidation process occurring at that electrode,termed the anode (hereinafter, “anodic processes”), and a second onethat consumes electrons by virtue of a reduction process occurring atthat electrode, termed the cathode (hereinafter, “cathodic processes”).

There are two broad classifications of batteries, primary batteries andsecondary batteries. In primary batteries, either the anodic process, orthe cathodic process, or both are irreversible, as defined forelectrochemical processes. For this reason, once the reagentsparticipating in the reactions are by-and-large consumed, the batterycan't be returned to a charged state by electrochemical means.

In secondary batteries the electron producing and consuming reactionsare for the most part reversible, as defined for electrochemicalprocesses, and therefore such a battery can be cycled between a chargedand discharged state electrochemically.

The reactions employed in batteries to produce and consume electrons areredox reactions. A pair of such reactions is called a redox couple. Eachredox reaction is termed a half cell, with two half cells constituting asimple battery when the half cells are placed in ionic communicationsuch that voltage potential appears between the electrodes of the halfcells. Typically, the electrodes of several sets of half cells areelectrically coupled together in either series or parallel configurationto supply a greater voltage or a greater current, or both than thatwhich is available from a single set of half cells.

The voltage potential of a simple battery (a single set of half cells)is fixed by the set of redox couples chosen to produce and consumeelectrons. The redox couples are chosen such that the potential energyof the electron producing reaction yields electrons of sufficientpotential energy to supply electrons to the electron consuming reaction.The electromotive force (emf) supplied by the battery is the differencebetween the potential energy of the electrons produced by the electronproducing reaction and that required of the electrons consumed by theelectron consuming reaction. As electrons are transferred from theelectron producing reaction to the electron consuming reaction, chargewithin the half cells in which these reactions are carried out isbalanced by the movement of ions between the half cells.

Ion batteries utilize materials in their construction that exhibit lowresistance to ion movement through and within their structure. Thus, ionbatteries improve the efficiency of storing and transferring electricalenergy by reducing the resistance that ions must overcome at theinterfaces of the various phases within the battery, and improve energystorage capacity by utilizing materials which do not polarize, andtherefore during charge movement do not build up space charge regionswhich contribute resistance to charge movement within the battery. Thisfeature tends to permit a higher density of charge species to be movedwithin a given volume of an ion battery than is possible withconventional materials. Additionally, thin film techniques permit theformation of very thin electrolyte layers separating the redox couples,further reducing resistance to charge movement within the batterystructure. Thin film ion batteries hold the promise of much higherenergy densities than are possible from conventional wet chemistrybatteries.

Ion batteries can be prepared from macroscopic compounding techniques tofabricate anode, cathode, and electrolyte materials which are thenbonded together to form the battery (the so called “thick film”technique), or by depositing thin films of such materials using vacuumtechniques, producing “thin film” batteries. The fabrication ofbatteries by “thick film” techniques is usually directed toward highcurrent capacity devices. Thin film batteries are generally employed inlow current draw applications in which space and weight must beconserved.

U.S. Pat. No. 5,895,731 (hereinafter “the '731 patent) to Clingempeel isexemplary of batteries fabricated using “thick film” construction. The'731 patent teaches the preparation of a cathode from a mixture ofpowders of titanium nitride, selenium, silicon, and buckminsterfullerenebonded together with epoxy polymer to aluminum foil. Additionally the'731 patent teaches the preparation of an anode from lithium foil,fiberglass matting and n-methyl-pyrrollidone, and the preparation of anelectrolyte layer by gelation of a mixture of n-methyl-pyrrollidone,lithium metal, and polyimide powder to produce a cross-linked lithiumgel electrolyte which is cast into a sheet. These materials are pressedtogether and sealed in polyimide plastic with appropriate electricalcontacts to the anode and cathode. Production of such a battery requiresstrict atmospheric control during fabrication to exclude moisture andoxygen, and numerous preparatory steps.

Thin film battery fabrication techniques are well known to those skilledin the art. Thus, for example, U.S. Pat. No. 5,338,625 to Bates(hereinafter “the '625 patent”), teaches the formation of a lithiumbased thin film battery by vacuum deposition of two co-planar vanadiumcurrent collectors on an insulating substrate. Upon one of the currentcollectors is deposited a cathode comprising an amorphous vanadium oxidelayer. This cathode layer is deposited by reactive ion sputtering from avanadium target in an oxygen environment. On top of the cathode layer isdeposited an amorphous lithium phosphorous oxynitride (also called“Sub-stoichiometric lithium phosphorous oxynitride”) layer which acts asan electrolyte. This layer is deposited by reactive ion sputtering oflithium orthophosphate in a nitrogen atmosphere. Finally, a layer oflithium metal was vacuum evaporated onto the assembly, covering both thebare current collector and the current collector bearing the cathode andelectrolyte. The disclosed thin film battery contains a bare lithiumanode, and as such requires further steps to isolate the anode from theambient environment. Additionally, because of the presence of therelatively low melting lithium metal the disclosed battery has lowtolerance for heating.

Hybrid batteries containing a combination of elements prepared bymacroscopic compounding techniques which in turn have thin filmsdeposited onto them have also been described. Thus, U.S. Pat. Nos.5,569,520 (hereinafter “the '520 patent”)and 5,612,152 (hereinafter “the'152 patent ”), both to Bates, describe a preparation of a lithiummanganate cathode pellet using traditional ceramic processing techniques(e.g., hot pressing and sintering the powder). The pellet is thensubjected to deposition of a thin electrolyte film of, e.g., lithiumphosphorous oxynitride (Sub-stoichiometric lithium phosphorousoxynitride), by reactive ion sputtering using the techniques describedabove for the '625 patent to Bates. A lithium film anode is thendeposited on the exposed face of the electrolyte film, again by vacuumtechniques, forming a multilayered thin film battery. The '520 and '152patents further disclose that an additional mass of lithium can beincorporated into the battery by sandwiching the anode of themulti-layered battery material described above with an additional sheetof lithium foil and cycling the sandwiched construction through severalcharging/discharging cycles. In this process, the thin lithium film is“plated” onto the foil sandwiched with it to form a continuous phasewith the electrolyte/lithium metal interface, bonding the lithium foilinto the multi-layered material.

The '152 and '520 patents further disclose that deposition of a lithiumanode film on the exposed face of the electrolyte of a multi-layerbattery material can be eliminated for the process of bonding a foilsandwiched to the multi-layer battery material. These patents disclosethat pressing a piece of lithium foil against the exposed face of theelectrolyte layer of the multi-layer battery material and cycling thebattery between charged and discharged states will also bond the lithiumfoil to the multi-layer battery material by virtue of deposition oflithium metal from the electrolyte during battery charging onto the faceof the lithium foil in contact with the electrolyte.

Finally, the '152 and '520 patents teach that deposition of an anode canbe dispensed with. Batteries can be fabricated by vacuum application ofan electrolyte film onto a cathode material and the application of acurrent collector onto the exposed side of the electrolyte film. Cyclingthe battery through a charge cycle electrochemically deposits a lithiumanode layer between the current collector and the electrolyte. Thus, athin film of Sub-stoichiometric lithium phosphorous oxynitride wasdeposited by vacuum evaporation onto a Li₂MnO₄ cathode pellet, forming aSub-stoichiometric lithium phosphorous oxynitride film coating on oneface of the cathode. Onto the exposed face of the Sub-stoichiometriclithium phosphorous oxynitride film coating a current collecting layerof vanadium metal was deposited. This multi-layer battery material wassubjected to a charging current, whereupon lithium metal was extractedfrom the electrolyte layer and plated onto the face of the vanadiumcurrent collector in contact with the electrolyte film.

Additional disclosure of the technique of electrochemical deposition ofa lithium metal anode within the multi-layer structure of an electrolyteand cathode material has been described in PCT application US00/06997 ofLockheed Martin Energy Research Corporation, filed 17 Mar. 2000(hereinafter, “the '997 application”). This application teaches theformation of a multi-layer battery material by sequential deposition ofvarious thin films onto an insulating substrate. In this manner, acathode current collector in the form of an Ag or Pt thin film was firstdeposited onto an alumina substrate. Following this a cathode film ofLi₂MnO₄ was deposited onto the current collector by vacuum sputteringtechniques. Onto the cathode film was deposited an electrolyte thin filmof Sub-stoichiometric lithium phosphorous oxynitride by reactive ionsputtering. Onto the exposed face of the Sub-stoichiometric lithiumphosphorous oxynitride electrolyte film was deposited a metal thin filmto serve as an anode current collector. The metal was selected frommetals that do not form intermetallic compounds with lithium, generallythe group 8 transition metals, Ti, aluminum, gold, and in particular therefractory metals, as will be known to one skilled in the art.

Thus fabricated, this multi-layer battery material was subject to acharging current whereby a lithium anode was plated between the currentcollector thin film and the electrolyte. The '997 application furtherteaches that a protective layer must be deposited onto the currentcollector for the electrochemical anode deposition/stripping to bereversible. In this role, deposition of films of lithium nitride orSub-stoichiometric lithium phosphorous oxynitride onto the exposed faceof the anode current collector film as protective layers is taught. The'997 application discloses that this over-layer functions to preventlithium chemical attack upon the current collector, prevent undesirablemorphology from occurring in the deposited lithium layer (a so called“fluffy” or “mossy” morphology), and to absorb the volume change thoughtto accompany the deposition of the lithium metal layer. The over-layeris said to additionally impart electrical insulation, mechanicalprotection, and act as a barrier to moisture and oxygen for the lithiumlayer.

While the plated lithium anode prior art has addressed some of theproblems associated with the Li/LiM_(x)O_(y) couple (where M=atransition metal), such as the heat sensitivity of lithium metal andsome of the difficulties due to the air sensitive nature of lithium (seeU.S. Pat. No. 5,871,865 to Barker et. al. for a discussion of these andother problems arising from the presence of lithium metal in thepreparation of batteries) there is still some inherent instability inlithium based batteries constructed according to disclosures in theprior art. This instability can be addressed by the addition of aprotective layer to the anode current collector. Such a solutionincreases the bulk of a battery, reducing its current density, and addsa processing step, increasing its cost, without increasing the netcapacity or performance of the battery.

The process of the present invention for production of a multi-layerthin film battery precursor structure is directed to eliminating theneed for an additional protective layer applied to the anode or anodecurrent collector and to increasing the amount of lithium that may beelectrochemically formed as an anode during activation of an “anodeless”battery precursor in the manner of Bates.

The present invention is directed toward minimizing the number ofprocessing steps required to fabricate a thin film battery, and atincreasing charge retention in a battery and the number ofcharge/discharge cycles that a battery can be subjected to withoutsignificant degradation. Additonally, the present invention seeks toprovide a method of producing a lithium based battery which is airstable without the application of a protective overlayer following theformation of the anode, cathode, and electrolyte layers and charging ofsuch a battery.

One aspect of the present invention is a process of producing asecondary, lithium based, thin film battery, having the steps of:

a) depositing a film comprising a solid state electrolyte material thatis a conductor of lithium ions onto an exposed, conductive face of asubstrate;

b) depositing a film of a transition metal oxide onto the electrolytematerial;

c) forming a cathode film layer by lithiating the transition metal oxidefilm until it contains a supra-stoichiometric amount of lithium;

d) depositing an electron-conductive current collector film upon thecathode film layer;

e) forming a lithium metal buried anode layer between the conductiveface of the substrate and the solid state electrolyte material using aflowing current between the substrate conductive face and the cathodecurrent collector, in the process oxidizing the cathode film layer andcausing lithium ions to migrate into and through the solid stateelectrolyte material, and then to be reduced to lithium metal andforming said buried anode layer; and

f) maintaining the current flow until the buried anode layer contains adesired amount of lithium metal.

Another aspect of the present invention are lithium thin film batterieswith buried anodes and reverse structures made according to the aboveprocess.

Another aspect of the present invention is a process for producing alithium based, thin film battery precursor composite structure,comprising the steps of:

a) depositing a film comprising a solid state electrolyte material thatis a conductor of lithium ions onto an exposed, conductive face of asubstrate;

b) depositing a film comprising a transition metal oxide on top of thefilm of solid state electrolyte material;

c) forming a cathode film layer by lithiating the transition metal oxidefilm until it contains a supra-stoichiometric amount of lithium; and

d) depositing a current collector film upon an exposed face of saidcathode film layer, said current collector comprising an electronconducting material.

Another aspect of the present invention are lithium battery precusorcomposite structures made according to the process for producing batteryprecursor composite structures recited above.

Another aspect of the present invention is a lithium battery compositeprecursor, characterized by its ability to form a buried lithium anodelayer at the interface between an anode current collector and anelectrolyte when a current is maintained between the anode currentcollector and the cathode current collector, and its ability to bechemically stable when exposed to an ambient environment, the precursorhaving an anode current collector layer that forms a support and has atleast one conductive face; an electrolyte layer that is a conductor oflithium ions and has one face in communication with a conductive face ofthe anode current collector layer; a cathode layer that is incommunication with a face of the electrolyte layer that is not incommunication with the anode current collector layer; and a cathodecurrent collector layer that is in communication with a face of thecathode layer that is not in communication with the electrolyte layer.

Another aspect of the present invention is a lithium thin film batteryhaving an anode current collector layer that forms a support and has atleast one conductive face; a buried anode layer comprising lithium metalin communication with a conductive face of said anode current collector;an electrolyte that is a conductor of lithium ions and is incommunication with said anode layer; a cathode layer that is incommunication with a face of said electrolyte layer that is not incommunication with said anode layer; and a cathode current collectorlayer that is in communication with a face of the cathode layer that isnot in communication with the electrolyte layer, the battery beingcharacterized by an increase in the amount of metallic lithium containedin its buried anode layer upon charging and a reduction in the amount oflithium metal in its buried anode layer upon discharging, and itschemical stability when exposed to an ambient environment in any stateof charge.

Other aspects of this invention will appear from the followingdescription and appended claims, reference being made to theaccompanying drawings forming a part of this specification wherein likereference characters designate corresponding parts in the several views.

BRIEF DESCRIPTION OF DRAWINGS

Before explaining the disclosed embodiments of the present invention indetail, it is to be understood that the invention is not limited in itsapplication to the details of the particular arrangement shown, sincethe invention is capable of other embodiments. Also, the terminologyused herein is for the purpose of description and not of limitation.

FIG. 1: A Deposition Sequence Resolved Cross-Sectional Elevation View Ofa Prior Art Thin Film Battery.

FIG. 2: A Cross-Sectional Elevation View Of a Battery PrecursorComposite Structure.

FIG. 3: A Cross-Sectional Elevation View Of a Thin Film Battery FormedBy Activation Of a Precursor Composite Structure.

FIG. 4: A Graph of the Charge Capacity of a Battery of the PresentInvention as a Function of Charge/Discharge Cycle Number.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed to a lithium based thin film secondarybattery. The thin film battery of the present invention can befabricated by sequential vapor deposition techniques to effect theapplication of the several film layers required to form a complexstructure (herein after, “battery precursor composite structure”). Thebattery precursor composite structure is then subjected to an activationstep, and thereafter functions as a thin film lithium based battery.

The process of the present invention utilizes three vapor depositionsteps to produce an air stable composite structure having a currentcollector layer, a cathode layer, and an electrolyte layer upon aconductive substrate. The order of these layers, as viewed from theconductive substrate, is reversed from that of conventional thin filmbatteries, which will be further elucidated below. The conductivesubstrate of the battery precursor composite structure serves as both asupport for the precursor composite structure and, upon activation, asan anodic current collector in the resultant thin film battery. Thevarious layers comprising the present invention battery structure can bedeposited using one or more such techniques as will be familiar to oneskilled in the art, for example, evaporation, sputtering, chemical vapordeposition, and the like.

The battery precursor composite structure is both oxygen and water vaporstable and thermally robust. As a consequence the battery precursorcomposite structure can be manipulated without isolation from theambient environment and can withstand the elevated temperaturesassociated with electronic device processing. Thus, for example, thebattery precursor composite structure of the present invention canwithstand incorporation into circuit boards or other electronic orelectrical subassemblies prior to soldering and/or encapsulation of thesubassembly without utilizing any special environment, isolation steps,or heat sinking devices to protect it.

The battery precursor composite structure can be activated using aninitial charging step in which a lithium metal anode is formed betweenthe support and the electrolyte, thereby producing a lithium-based thinfilm battery which is characterized by having the lithium metal layerburied in the structure of the battery (hereinafter, “buried anodestructure”) and requiring no additional layer to protect it from theambient environment. This battery can be returned to the batteryprecursor composite structure state by completely discharging it,thereby consuming the anode and returning it to its “as deposited”battery precursor composite structure state.

With reference to FIG. 1, the prior art preparation of lithium basedthin film secondary batteries begins with a substrate 100, typically aninsulator comprising a metal oxide, upon which is deposited a cathodeconductive current collector layer 101. The cathode current collector ischosen for high conductivity and chemical inertness, and is typically ametal. Metals used in the prior art for this purpose include platinum orgold.

Onto current collector layer 101 is deposited a cathodic electrodematerial 102. Cathodic electrode material 102, in the case of a lithiumbattery, is typically a lithium intercalation compound capable ofreversibly ejecting lithium ions as the compound is oxidized, andinjecting lithium ions as the compound is reduced. Examples of suchcompounds are lithium manganate (LiMn₂O₄), lithium nickelate (LiNiO₂),and lithium vanadate (LiV₂O₅). Other lithiated transition metal oxideshave also been employed for this purpose.

Next, a solid state electrolyte layer 103 is deposited upon the cathodicelectrode layer 102. Solid electrolyte 103 is chosen for its stabilityin contact with lithium metal and its ability to be a facile conductorof lithium ions between cathode 102 and anode 104. Typically,substoichiometric lithium phosphorous oxynitride is used as anelectrolyte layer. Substiochiometric lithium phosphorous oxynitride is afamily of materials having the general formula Li_(x)PO_(y)N_(z). In the“as deposited” state, the material has values for x and y of about 3,and for z of about 1.5.

Onto electrolyte layer 103 is next deposited a layer of lithium metalwhich serves as anode 104. Some prior art devices include a barrierlayer 107, chosen to be impermeable to Li atoms, is interposed betweenelectrolyte layer 103 and lithium metal anode 104. The barrier layerprevents chemical attack upon the electrolyte layer by Li. In the casewhere Sub-stoichiometric lithium phosphorous oxynitride is chosen as theelectrolyte layer, barrier layer 107 is not needed.

Anode layer 104 is next deposited, either onto the exposed face ofbarrier layer 107, if it is used, or directly onto the exposed face ofelectrolyte layer 103, if barrier layer 107 is not used. In a lithiumbased battery, anode layer 104 is a lithium metal thin film.

Anode current collector 105 is then deposited onto anode 104. The anodecurrent collector is chosen to preclude formation of lithiumintermetallic compounds, and is selected from group 8 transition metals,Ti, and noble metals.

Finally, anode protection layer 106 is deposited onto current collectorlayer 105. Anode protection layer 106 is typically a second layer ofSub-stoichiometric lithium phosphorous oxynitride or another moistureand electron impervious layer such as AlN. A typical thin film batteryrequires between five and seven deposition steps, at least one of whichis carried out primarily to shield battery elements comprised of lithiummetal from the ambient environment.

The sequence of the prior art deposition steps is chosen to minimize theproblems associated with having a thermally labile and reactive species,such as lithium metal present during deposition of subsequent layers, aswould be the case if the above described deposition sequence were to bereversed, with a layer of lithium metal being deposited first and theremaining layers deposited on top of it.

If the lithium metal anode is eliminated, the prior art teaches that onemay be formed electrochemically “in situ” by utilizing lithium containedin the cathode material. Such a scheme does not permit the formation ofanodes with lithium present in supra-stoichiometric amounts relative tothe cathodic material. Because the amount of lithium which can beincorporated into the anode is limited in this manner, the volumetricenergy capacity of the battery can't be maximized. Additionally, theprior art suggests that the overlayer material must be selected toprovide for volume changes in the anode layer during charging anddischarging and to prevent undesirable morphology in the anode materialas it is formed. If this is not done, battery failure will followcharging and discharging of the battery.

With reference to FIG. 2, the deposition of a reverse structure batteryprecursor composite structure 200 can be carried out in three depositionsteps, building the functional layers up upon the anode currentcollector of the device. Thus, anode current collector (hereinafter,“substrate”) 201 is chosen for its electrical conductivity and its inertcharacter toward attack by lithium metal, as well as its ability tofunction as a support for the other layers deposited onto it. Substrate201 may be, for example, a refractory metal, examples of which arecopper and nickel. Substrate 201 may also be a ferrous alloy, forexample steel, by way of example, stainless steel, for example type 430,also designated as ASTM A176 and type 304, also designated as type A167,which are articles of commerce recognized by those of ordinary skill inthe art as an alloy which comprises also chrome. Substrate 201 may alsobe a layer of any other conductive metal that is compatible with lithiummetal, for example iron, or any transition metal that does not formintermetallic compounds with lithium. Substrate 201 can also comprise anon-electrical conductor, for example glass or a plastic, such as willbe familiar to those of ordinary skill in the art, for example,polyester onto which a conductive film has been deposited, for examplegold.

Onto substrate 201 is deposited an electrolyte film layer 204.Electrolyte film layer 204 is chosen for its ability to be a facileconductor of lithium ions and for its stability when in contact withlithium metal. The electrolyte may be any solid state electrolyte thatcan be deposited by vacuum techniques that fulfills the criterion offacile lithium ion conduction and inertness toward lithium metal, butthe preferred electrolyte is lithium phosphorous oxynitride(Sub-stoichiometric lithium phosphorous oxynitride) as defined above.

Onto the exposed face of electrolyte film 204 (the face of the filmlayer that is not in contact with substrate 201) is deposited cathodelayer 203. The material from which cathode layer 203 is formed may beany of the lithium intercalate materials which can reversibly ejectlithium ions upon (LiMn₂O₄), lithium nickelate (LiNiO₂), and lithiumvanadate (LiV₂O₅). These films can be deposited from sources containinglithium with subsequent elimination of the lithium insertion step, orfrom the transition metal oxide which is then subjected to a lithiuminsertion step.

The preferred method of fabricating cathode layer 203 is to deposit atransition metal oxide layer of desired thickness followed by lithiationof the transition metal oxide. This process permits a cathode layer 203thus formed to contain a supra-stoichiometric amount of lithium whichcan be made available for formation of a lithium anode when batteryprecursor composite structure 200 is subjected to an activation step(described below). Lithiation of the oxide film can be accomplished bytreating the transition metal oxide film with lithium vapor. It will beappreciated by one of skill in the art, that a transition metal oxidecontaining supra-stoichiometric amounts of lithium is more stable uponthermal exposure and upon exposure to the ambient environment thanstructures of the same type containing free lithium metal layers.

The preferred transition metal from which the oxide layer is formed isvanadium. A suitable vanadium oxide-based cathode layer 203 can beformed by first depositing a layer of V₂O₅ onto the exposed face ofelectrolyte layer 204 by, for example, reactive ion sputtering from avanadium target in the presence of oxygen. Following this step, lithiummetal can be vacuum evaporated onto the vanadium oxide layer, thuslithiating the oxide layer.

Other vacuum techniques as will be familiar to one skilled in the artcan be employed to deposit various layers of the present inventionbattery. In particular, several techniques familiar to those of skill inthe art can be used to deposit cathode layer 203, both in cases wherethe layer is a stoichiometric lithium transition metal oxide, and incases where the layer contains a supra-stoichiometric amount of lithiummetal.

In a fourth step following two film deposition steps and the lithiationstep, a cathode current collector film 202 is deposited onto cathodefilm 203. Although cathode current collector film 202 may be anyelectrically conductive metal that is inert toward the cathode material,aluminum and copper are preferred.

A battery of the type shown in cross-section in FIG. 3 is formed byactivating the multi-layer battery precursor composite structure 200.Multi-layer battery precrsor composite structure 200 is activated byapplying a source of sufficient electromotive force (emf) of constantpolarity between substrate 201 and the cathode current collector layer202. With reference to FIG. 3, in this manner, material in cathode layer203 is oxidized. During this oxidation, lithium ions are ejected fromcathode layer 203 and are conducted through the electrolyte layer 204.The lithium ions are subsequently electrochemically reduced to lithiummetal at the electrolyte 204/support 201 interface, thus forming theburied lithium metal anode layer 305. This layer is termed buriedbecause it is formed in such a manner that it is never exposed to theambient environment, but is instead formed within the structure of thebattery precursor composite material, and protected afterward by thethick conductive support 200 beneath it (as FIG. 3 is drawn) and by theother multiple layers above it. Current is passed into the device inthis manner until a lithium anode layer of sufficient thickness has beenformed.

Once the activation step is completed, thus depositing buried anodelayer 305 of the desired thickness, battery 300 has a configurationwhich is inverted from that of the conventional lithium thin filmbattery (hereinafter, “reverse configuration”). This reverseconfiguration provides for a “buried anode” structure that both protectsthe anode, without additional protective layers, and provides for abattery that withstands exposure to the ambient environment and canwithstand thermal excursions without deterioration.

EXAMPLE 1

A coupon of type 430 stainless steel (an article of commerce also knownto those of ordinary skill in the art as ASTM A176, an alloy having 16wt. % chromium or more) was cut firm sheet stock obtained from TeledyneRodney Metals, Inc., New Bedford, Mass. The coupon was prepared for useas an anode current collector/substrate 201 by washing the stainlesssteel in a detergent solution, rinsing with deionized water, followed byan additional ethyl alcohol rinse, and drying in room air. The detergentemployed was Alkanox, a commercial detergent for cleaning laboratoryglassware, but any neutral detergent formulated for such purpose canalternatively be employed.

Thus prepared, the substrate was placed into a vacuum chamber containinga target of Li₃PO₄. The chamber was evacuated to 10⁻⁵ torr and aSub-stoichiometric lithium phosphorous oxynitride film of 1.0 nm-thickelectrolyte layer 204 was formed upon the exposed face of the stainlesssteel substrate by reactive ion sputtering in 20 millitorr of nitrogengas using a RF power setting of 4-5 W/cm².

A 500 nm-thick cathode film 203 was next formed by first depositing avanadium oxide film onto the electrolyte film. This vanadium oxide thinfilm was deposited by thermal evaporation of a corresponding V₂O₃ powdersource.

Thus formed, the vanadium oxide layer was then lithiated by exposing thevanadium oxide layer to lithium vapor. Lithium vapor was obtained bythermal evaporation of pure Li metal onto the V₂O₅ layer at roomtemperature in a 10⁻⁵ mbar vacuum. Upon contact with the vanadium oxidefilm, lithium diffuses into the vanadium oxide material, forming alithium vanadium oxide cathode. Treatment with lithium vapor wascontinued until a material approximating the formula Li_(x)V₂O₅ wasobtained, wherein X ³3.

Onto the lithiated vanadium oxide layer was deposited a 200-300 nm layerof aluminum metal by vacuum evaporation to act as the cathode currentcollector 202.

Thus prepared, the multi-layered battery precursor composite structure200 was removed from the vacuum chamber and connected to a Arbinpotentio-galvanostat to apply a constant current and monitor voltagechanges. Current was applied to the multi-layered material until thecell voltage reached about 3.8 V vs. Li. In this manner a buried lithiumanode was created forming a thin-film battery which could be handled inthe ambient environment without further isolation. The dischargecapacity of this battery was about 25 mAh/cm² which corresponds to 1.4Li per mole of V₂O₅.

EXAMPLE 2

The battery device of Example 1 was subjected to cyclic testing for over750 charge/discharge cycles. This was accomplished by charging anddischarging the battery under conditions in which charging currenthaving a current density of 0.1 mA/cm² was applied until a potential ofabout 3.8 vs lithium was observed across the battery. Discharge cycleswere carried out at the same current density and continued until apotential of about 2.0 V vs lithium was observed across the battery. Theresults are presented in FIG. 4. It can be seen that the capacity of thebattery did not appreciably change in over 800 such charge/dischargecycles. The battery retained its ability to be handled in the ambientenvironment throughout the charge/discharge test.

Although the present invention has been described with reference topreferred embodiments, numerous modifications and variations can be madeand still the result will come within the scope of the invention. Nolimitation with respect to the specific embodiments disclosed herein isintended or should be inferred.

What is claimed is:
 1. A process for producing a secondary, lithium based, thin film battery, the process comprising the steps of: a) depositing a film comprising a solid state electrolyte material onto an exposed, conductive face of a substrate, wherein the solid state electrolyte material is a conductor of lithium ions; b) depositing a film of a transition metal oxide upon an exposed face of said film of solid state electrolyte material; c) lithiating said transition metal oxide film until it contains a supra-stoichiometric amount of lithium, thus forming a cathode film layer; d) depositing a current collector film upon an exposed face of said cathode film layer, said current collector comprising an electron conducting material; e) forming a buried anode layer comprising lithium metal between said conductive face of said substrate and said solid state electrolyte material by flowing a current between said substrate conductive face and said cathode current collector, whereby said cathode film layer is oxidized, causing lithium ions to migrate into and through said solid state electrolyte material, thence being reduced to lithium metal and forming said buried anode layer; and f) maintaining said current flow until said buried anode layer contains a desired amount of lithium metal.
 2. The process of claim 1, wherein techniques used to deposit said films are selected from vacuum evaporation and reactive sputtering.
 3. The process of claim 1, wherein said solid state electrolyte film comprises Sub-stoichiometric lithium phosphorous oxynitride.
 4. The process of claim 3, wherein said cathode film is selected from lithium vanadate, lithium manganate, lithium nickelate, and lithium cobaltate.
 5. The process of claim 1, wherein said substrate is selected from stainless steel, plastic bearing a conductive coating on at least one face, and glass bearing a conductive coating on at least one face.
 6. The process of claim 1, wherein said cathode current collector is selected from aluminum, gold, and refractory metal.
 7. A process for producing a secondary, lithium based, thin film battery, the process comprising the steps of: a) depositing a film comprising a solid state electrolyte material onto an exposed, conductive face of a substrate, wherein the solid state electrolyte material is a conductor of lithium ions; b) depositing a cathode film comprising a lithiated transition metal oxide upon an exposed face of said film of solid state electrolyte material; c) depositing a current collector film upon an exposed face of said cathode film layer, said current collector comprising an electron conducting material; d) forming a buried anode layer comprising lithium metal between said conductive face of said substrate and said solid state electrolyte material by flowing a current between said substrate conductive face and said cathode current collector, whereby said cathode film layer is oxidized, causing lithium ions to migrate into and through said solid state electrolyte material, thence being reduced to lithium metal and forming said buried anode layer; and e) maintaining said current flow until said buried anode layer contains a desired amount of lithium metal.
 8. The process of claim 7, wherein techniques used to deposit said films are selected from vacuum evaporation and reactive sputtering.
 9. The process of claim 7, wherein said solid state electrolyte film comprises Sub-stoichiometric lithium phosphorous oxynitride.
 10. The process of claim 9, wherein said cathode film is selected from lithium vanadate, lithium manganate, litbium nickelate, and lithium cobaltate.
 11. The process of claim 7, wherein said substrate is selected from stainless steel, plastic bearing a conductive coating on at least one face, and glass bearing a conductive coating on at least one face.
 12. The process of claim 7, wherein said cathode current collector is selected from aluminum, gold, and refractory metals.
 13. A process for producing a secondary, lithium based, thin film battery, the process comprising the steps of: a) depositing a film comprising lithium phosphorous oxynitride on an exposed face of type 430 stainless steel substrate by reactive ion sputtering from a target of Li₃PO₄ in nitrogen, thereby forming a lithium phosphorous oxynitride electrolyte film bonded to one face of said stainless steel substrate; b) forming a cathode film comprising lithium vanadate bonded to an exposed face of said lithium phosphorous oxynitride; c) depositing a film comprising copper metal upon an exposed face of said lithium vanadate cathode film, thereby forming a cathode current collection bonded to said lithium vanadate cathode film; d) forming a buried anode layer comprising lithium metal between said stainless steel substrate and said lithium phosphorous oxynitride electrolyte film by flowing a current between said stainless steel substrate and said cathode current collector, whereby said cathode film layer is oxidized, causing lithium ions to migrate into and through said solid state electrolyte material, thence being reduced to lithium metal and forming said buried anode layer; and e) maintaining said current flow until said buried anode layer contains a desired amount of lithium metal.
 14. A process for producing a secondary, lithium based, thin-film battery, the process comprising the steps of: a) depositing a film comprising lithium phosphorous oxynitride on the exposed face of a type 304 stainless steel substrate by reactive ion sputtering from an LiPO₄ target in nitrogen, thereby forming a lithium phosphorous oxynitride electrolyte film bonded to said stainless steel substrate face; b) depositing a film comprising vanadium oxide upon an exposed face of said lithium phosphorous oxynitride film by thermal evaporation from vanadium oxide powder, thereby forming a vanadium oxide film bonded to said phosphorous oxynitride film; c) exposing said vanadium oxide film to lithium metal vapor, thereby forming a lithium vanadate cathode film; d) depositing a film comprising copper metal upon an exposed face of said lithium vanadate cathode film, thereby forming a cathode current collector bonded to said lithium vanadate cathode film; e) forming a buried lithium anode layer between said stainless steel substrate and said lithium phosphorous oxynitride electrolyte film by flowing a current between said substrate and said cathode current collector, whereby said lithium vanadate cathode film is oxidized, causing lithium ions to migrate into and through said lithium phosphorous oxynitride electrolyte film, thence being reduced to lithium metal and forming said buried anode layer; and f) maintaining said current flow until said buried anode layer contains a desired amount of lithium metal.
 15. The process of claim 14, wherein said vanadium oxide film is exposed to sufficient lithium vapor to form a film having the formula Li_(x)V₂O₅ where x is about 3 or greater.
 16. A process for producing a lithium based, thin film secondary battery precursor composite structure, the process comprising the steps of: a) depositing a film comprising a solid-state electrolyte material onto an exposed, conductive face of a substrate, wherein the solid state electrolyte material is a conductor of lithium ions; b) depositing a film comprising a transition metal oxide upon an exposed face of said film of solid state electrolyte material; c) lithiating said transition metal oxide film until it contains a supra-stoichiometric amount of lithium, thus forming a cathode film layer; and d) depositing a current collector film upon an exposed face of said cathode film layer, said current collector comprising an electron conducting material.
 17. The process of claim 16, wherein techniques used to deposit said films are selected from vacuum evaporation and reactive sputtering.
 18. The process of claim 16, wherein said solid state electrolyte film is sub-stoichiometric lithium phosphorous oxynitride.
 19. The process of claim 18, wherein said cathode film layer is selected from lithium vanadate, lithium manganate, lithium nickelate, and lithium cobaltate.
 20. The process of claim 16, wherein said substrate is selected from stainless steel, plastic bearing a conductive coating on at least one face, and glass bearing a conductive coating on at least one face.
 21. The process of claim 16, wherein said cathode current collector is selected from aluminum, gold, and refractory metals.
 22. A process for producing a lithium based, thin film secondary battery precursor composite structure, the process comprising the steps of: a) depositing a film comprising a solid state electrolyte material onto an exposed, conductive face of a substrate, wherein the solid state electrolyte material is a conductor of lithium ions; b) depositing a cathode film comprising lithiated transition metal oxide upon an exposed face of said film of solid state electrolyte material; and c) depositing a current collector film upon an exposed face of said cathode film layer, said current collector comprising an electron conducting material.
 23. The process of claim 22, wherein techniques used to deposit said films are selected from vacuum evaporation and reactive sputtering.
 24. The process of claim 22, wherein said solid state electrolyte film is sub-stoichiometric lithium phosphorous oxynitride.
 25. The process of claim 24, wherein said cathode layer is selected from lithium vanadate, lithium manganate, lithium nickelate, and lithium cobaltate.
 26. The process of claim 22, wherein said substrate is selected from a stainless steel, a plastic bearing a conductive coating on at least one face, and a glass bearing a conductive coating on at least one face.
 27. The process of claim 22, wherein said cathode current collector is selected from aluminum, gold, and refractory metals.
 28. A process for producing a lithium based, thin film secondary battery precursor composite structure, the process comprising the steps of: a) depositing a film comprising lithium phosphorous oxynitride on an exposed face of a type 430 stainless steel substrate by reactive ion sputtering from a target of Li₃PO₄ in nitrogen, thereby forming a lithium phosphorous oxynitride electrolyte film bonded to one face of said stainless steel substrate; b) forming a cathode film comprising lithium vanadate bonded to an exposed face of said lithium phosphorous oxynitride; and c) depositing a film comprising copper metal upon an exposed face of said cathode film, thereby forming a cathode current collector bonded to said lithium vanadate cathode film.
 29. A process for producing a lithium based, thin film secondary battery precursor composite structure, the process comprising the steps of: a) depositing a film comprising lithium phosphorous oxynitride on the exposed face of a type 430 stainless steel substrate by reactive ion sputtering from an Li₃PO₄ target in nitrogen, thereby forming a lithium phosphorous oxynitride electrolyte film bonded to said stainless steel substrate face; b) depositing a film comprising vanadium oxide upon an exposed face of said lithium phosphorous oxynitride film by thermal evaporation from vanadium oxide powder, thereby forming a vanadium oxide film bonded to said phosphorous oxynitride film; c) exposing said vanadium oxide film to lithium metal vapor, thereby forming a lithium vanadate cathode film; and d) depositing a film comprising copper metal upon an exposed face of said lithium vanadate cathode film, thereby forming a cathode current collector bonded to said lithium vanadate cathode film.
 30. The process of claim 29, wherein said vanadium oxide film is exposed to sufficient lithium vapor to form a film having a composition Li_(x)V₂O₅, where x is about 3 or greater.
 31. The process of claim 3, wherein said cathode film is lithium vanadate.
 32. The process of claim 3, wherein said cathode film is lithium manganate.
 33. The process of claim 3, wherein said cathode film is lithium nickelate.
 34. The process of claim 3, wherein said cathode film is lithium cobaltate.
 35. A lithium based, thin film secondary battery precursor composite structure produced by the process comprising the steps of: a) depositing a film comprising a solid state electrolyte material onto an exposed, conductive face of a substrate, wherein the solid state electrolyte material is a conductor of lithium ions; b) depositing a film comprising a transition metal oxide upon an exposed face of said film of solid state electrolyte material; c) lithiating said transition metal oxide film until it contains a supra-stoichiometric amount of lithium, thus forming a cathode film layer; and d) depositing a current collector film upon an exposed face of said cathode film layer, said current collector comprising an electron conducting material.
 36. A secondary, lithium based, thin film battery produced by the process comprising the steps of: a) depositing a film comprising a solid state electrolyte material onto an exposed, conductive face of a substrate, wherein the solid state electrolyte material is a conductor of lithium ions; b) depositing a film of a transition metal oxide upon an exposed face of said film of solid state electrolyte material; c) lithiating said transition metal oxide film until it contains a supra-stoichiometric amount of lithium, thus forming a cathode film layer; d) depositing a current collector film upon an exposed face of said cathode film layer, said current collector comprising an electron conducting material; e) forming a buried anode layer comprising lithium metal between said conductive face of said substrate and said solid state electrolyte material by flowing a current between said substrate conductive face and said cathode current collector, whereby said cathode film layer is oxidized, causing lithium ions to migrate into and through said solid state electrolyte material, thence being reduced to lithium metal and forming said buried anode layer; and f) maintaining said current flow until said buried anode layer contains a desired amount of lithium metal. 